Bandwidth allocation device and bandwidth allocation method

ABSTRACT

A bandwidth allocation device is included in a communication system having a terminal station device and a terminal device and relaying upstream data, which is received from a communication terminal by a lower device connected to the terminal device, to an upper device connected to the terminal station device. The bandwidth allocation device includes a transmission-permitted period start position determining unit configured to estimate a start position of an arrival period in which the upstream data arrives at the terminal device from the lower device; a transmission-permitted period length determining unit configured to estimate a length of the arrival period based on an amount of upstream data to be transmitted from the lower device to the terminal device; and a bandwidth allocation unit configured to allocate a bandwidth to the terminal device based on the estimated start position and the estimated length of the arrival period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Phase of InternationalApplication No. PCT/JP2018/004046, filed on Feb. 6, 2018, which claimspriority to Japanese Application No. 2017-023365, filed on Feb. 10,2017. The entire disclosures of the above applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a bandwidth allocation device and abandwidth allocation method.

BACKGROUND ART

In the time division multiplexing-passive optical network (TDM-PON) suchas next generation-passive optical network 2 (NG-PON2), terminal device(an optical network unit (ONU)) receives upstream data from a lowerdevice and also transmits a signal (hereinafter referred to as “requiredtransmission amount notification”) representing bandwidth information (arequired transmission amount) necessary to transmit the upstream data toterminal station device (an optical line terminal (OLT)). Afterreceiving required transmission amounts from all ONUs through requiredtransmission amount notifications, the OLT determines a bandwidthallocation amount (hereinafter referred to as “allocation amount”) foreach ONU on the basis of the corresponding required transmission amountand transmits a signal for providing a notification of the allocationresult (hereinafter referred to as “transmission allocation amountnotification signal”) to each ONU. Each ONU transmits upstream datawhich can be transmitted in a transmission bandwidth designated by thetransmission allocation amount notification signal on the basis of adesignated allocation amount.

Due to this allocation control, after ONUs notify the OLT of requiredtransmission amounts for upstream data received from lower devices,allocation amounts for upstream data transmission to the ONUs aredetermined by the OLT, and each ONU is notified of an allocation amount.Because of such control, it takes time to transmit upstream data, whichcauses a delay (hereinafter referred to as “control delay”). Thiscontrol delay becomes a bottleneck in low-latency transmission which isrequired when a mobile wireless communication system is accommodated ina TDM-PON system. So far, the following two methods have been disclosedto reduce the corresponding control delay.

One method is to reduce control delay in cooperation with an upperdevice (e.g., see Non-Patent Document 1). In a mobile wirelesscommunication system, an upper device performs scheduling at everytransmission time interval (TTI) so that the upper device may centrallycontrol upstream transmission from a user terminal which is wirelesslyconnected to a lower device. The scheduling results are transmitted toeach user terminal, and each user terminal performs upstreamtransmission on the basis of the corresponding scheduling result.Hereinafter, upstream user data transmitted from a user terminal is alsoreferred to as “mobile data.” According to the method of Non-PatentDocument 1, an OLT receives in advance, from an upper device, wirelessresource information including information for specifying at least theamount of upstream user data received from each user terminal by a lowerdevice (hereinafter referred to as “mobile data amount”) and thereception time (hereinafter referred to as “mobile data receiving time”)among the scheduling results. The OLT determines an allocation amountfor each ONU on the basis of the corresponding information and notifieseach ONU of the corresponding allocation amount. In this way, the OLTcan determine an allocation amount without waiting for a requiredtransmission amount notification from each ONU, and thus control delaycan be reduced.

The other method is to statistically determine the allocation amount(e.g., see Non-Patent Document 2). According to this method, an OLTmonitors the amount of upstream data (traffic amount) transmitted fromeach ONU and determines an allocation amount for each ONU on the basisof a statistical value of monitoring results. For this reason, like inNon-Patent Document 1, the OLT becomes able to determine an allocationamount without waiting for receiving a required transmission amountnotification from each ONU, and thus control delay can be reduced.

CITATION LIST Non Patent Literature

-   [Non-Patent Document 1]-   T. Tashiro, et al., “A Novel DBA Scheme for TDM-PON based Mobile    Fronthaul,” OFC 2014, Tu3F.3, 2014-   [Non-Patent Document 2]-   T. Kobayashi, et al., “Bandwidth Allocation scheme based on Simple    Statistical Traffic Analysis for TDM-PON based Mobile Fronthaul,”    OFC 2016, W3C.7, 2016

SUMMARY OF INVENTION Technical Problem

In a prior art, FIG. 18A and FIG. 18B are diagrams showing arelationship between a transmission-permitted period for an ONU and anarrival period of mobile data. The transmission-permitted period is aperiod in which an ONU is permitted to transmit upstream data. In anideal state shown in FIG. 18A, a period in which mobile data arrives atan ONU (hereinafter referred to as “mobile data arrival period”) isincluded in a transmission-permitted period allocated to the ONU in theTTI. However, a processing latency in a lower device and a gap betweenpieces of mobile data are not included in either of wireless resourceinformation of Non-Patent Document 1 or a statistical value ofNon-Patent Document 2. For this reason, sometimes, it is not possible toinclude an entire mobile data arrival period in a transmission-permittedperiod. This means that there is mobile data which cannot be transmittedby an ONU in the TTI as shown in an unideal state of FIG. 18B.

In consideration of the above circumstances, an object of the presentinvention is to provide a bandwidth allocation device and a bandwidthallocation method for reducing the amount of upstream data which cannotbe transmitted from terminal device to terminal station device in onedata transmission interval.

Solution to Problem

According to a first aspect of the present invention, a bandwidthallocation device allocates a bandwidth to at least one terminal devicein a communication system including a terminal station device and the atleast one terminal device and relaying upstream data, which is receivedfrom a communication terminal by a lower device connected to the atleast one terminal device, to an upper device connected to the terminalstation device. The bandwidth allocation device includes atransmission-permitted period start position determining unit configuredto estimate a start position of an arrival period in which the upstreamdata arrives at the at least one terminal device from the lower device,a transmission-permitted period length determining unit configured toestimate the length of the arrival period on the basis of a data amountof upstream data that can be transmitted from the lower device to the atleast one terminal device, and a bandwidth allocation unit configured toallocate a bandwidth to the at least one terminal device on the basis ofthe estimated start position and the estimated length of the arrivalperiod.

According to a second aspect of the present invention, theabove-described bandwidth allocation device of the first aspect furtherincludes a cooperative processing unit configured to acquire radioresource information indicating radio resources allocated to thecommunication terminal for wireless communication with the lower devicefrom the upper device and calculate an arrival start time where theupstream data begins to arrive at the lower device on the basis of theradio resource information. The transmission-permitted period startposition determining unit is configured to treat a time obtained byadding at least a time spent for internal processing in the lower deviceto the arrival start time as an estimated time of the start position.

According to a third aspect of the present invention, theabove-described bandwidth allocation device of the first aspect furtherincludes a traffic monitoring unit configured to monitor the trafficamount of upstream data received from the at least one terminal deviceat the terminal station device. The transmission-permitted period startposition determining unit is configured to detect-a time at which theamount of upstream user data received from the at least one terminaldevice begins to exceed a threshold value in each autonomous intervalhaving a same length as a transmission time interval of the upstreamdata from the lower device to the upper device and is configured totreat a time obtained by adding a time difference between a start timein the autonomous interval and the detected time in the autonomousinterval to the start time in each autonomous interval at the terminalstation device as an estimated time of the start position.

According to a fourth aspect of the present invention, in theabove-described bandwidth allocation device of the first aspect, thetransmission-permitted period length determining unit is configured totreat a value obtained by multiplying a predetermined length of theperiod and a value obtained by dividing the amount of upstream data tobe transmitted from the lower device by a minimum arrival amount, whichis a minimum arrivable amount of upstream data from the lower device ina predetermined period, as an estimated value of the length of thearrival period.

According to a fifth aspect of the present invention, in theabove-described bandwidth allocation device of the fourth aspect, thetransmission-permitted period length determining unit is configured totreat a value obtained by multiplying a value obtained by dividing thepredetermined length of the period by a maximum length of the arrivalperiod and an transmittable amount of upstream data in the maximumlength of the arrival period as the minimum arrival amount.

According to a sixth aspect of the present invention, in theabove-described bandwidth allocation device of the fourth aspect, when avalue obtained by multiplying the predetermined length of the period anda value obtained by dividing an amount of upstream data to betransmitted from the lower device by the minimum arrival amount exceedsa length of a transmission time interval of the upstream data from thelower device to the upper device, the transmission-permitted periodlength determining unit is configured to treat the length of thetransmission time interval as the estimated value of the arrival period.

According to a seventh aspect of the present invention, in theabove-described bandwidth allocation device of the first aspect, thebandwidth allocation unit is configured to equally distribute abandwidth available in a period in which the at least one terminaldevice has the arrival period to the at least one terminal device havingthe arrival period in the period and is configured to equally distributea bandwidth available in a period in which any of the at least oneterminal device does not have the arrival period to all of the at leastone terminal device in the period.

According to an eighth aspect of the present invention, theabove-described bandwidth allocation device of the first aspect furtherincludes a control parameter estimation unit configured to determinewhether the at least one terminal device has upstream data to betransmitted to the upper device at each allocation cycle obtained bydividing a transmission time interval of the upstream data from thelower device to the upper device and estimate a processing latency inthe lower device on the basis of a start time of an allocation cycle inwhich it is determined a largest number of times that upstream data tobe transmitted to the upper device is present and a time at which thelower device receives the upstream data from the communication terminal.The transmission-permitted period start position determining unit isconfigured to calculate an estimated time of the start position on thebasis of the processing latency estimated by the control parameterestimation unit and the time at which the lower device receives theupstream data from the communication terminal.

According to a ninth aspect of the present invention, theabove-described bandwidth allocation device of the first aspect furtherincludes a control parameter estimation unit configured to acquire anamount of upstream data to be transmitted to the upper device from theat least one terminal device at each allocation cycle obtained bydividing a transmission time interval of the upstream data from thelower device to the upper device and estimate a minimum arrival amount,which is a minimum amount of upstream data to be arrived at the at leastone terminal device in an allocation cycle, on the basis of a differencein the amount of upstream data between allocation cycles. Thetransmission-permitted period length determining unit is configured totreat a value obtained by multiplying a length of an allocation cycleand a value obtained by dividing an amount of upstream data transmittedfrom the lower device to the at least one terminal device by the minimumarrival amount as an estimated value of the length of the arrivalperiod.

According to a tenth aspect of the present invention, in theabove-described bandwidth allocation device of the eighth aspect, thecontrol parameter estimation unit is configured to recursively divideallocation cycles in the transmission time interval into a first halfallocation cycle and a second half allocation cycle, the controlparameter estimation unit is configured to estimate a number of burstframes in the upstream data on the basis of a number of times ofdivision of the transmission time interval performed until a certaindifference or more is detected between an amount of upstream datatransmitted in the first half allocation cycle and an amount of upstreamdata transmitted in the second half allocation cycle, and thetransmission-permitted period start position determining unit isconfigured to calculate an estimated time of the start position on thebasis of the processing latency and the number of burst frames estimatedby the control parameter estimation unit and the time at which the lowerdevice receives the upstream data from the communication terminal.

According to an aspect of the present invention, a bandwidth allocationmethod executed by a bandwidth allocation device which is configured toallocate a bandwidth to at least one terminal device in a communicationsystem including a terminal station device and the at least one terminaldevice and relaying upstream data, which is received from acommunication terminal by a lower device connected to the at least oneterminal device, to an upper device connected to the terminal stationdevice includes a transmission-permitted period start positiondetermining step in which a transmission-permitted period start positiondetermining unit estimates a start position of an arrival period inwhich the upstream data arrives at the at least one terminal device fromthe lower device, a transmission-permitted period length determiningstep in which a transmission-permitted period length determining unitestimates a length of the arrival period on the basis of a data amountof upstream data that can be transmitted from the lower device to the atleast one terminal device, and a bandwidth allocation step in which abandwidth allocation unit allocates a bandwidth to the at least oneterminal device on the basis of the estimated start position and theestimated length of the arrival period.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce the amountof upstream data that cannot be transmitted from terminal device toterminal station device in one data transmission time interval.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of a transmission-permittedperiod according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of a communication system accordingto the first embodiment.

FIG. 3 is a flowchart showing a bandwidth allocation process of anallocation amount calculation unit according to the first embodiment.

FIG. 4 is a flowchart showing a transmission-permitted period startposition and transmission-permitted period length update process of theallocation amount calculation unit according to the first embodiment.

FIG. 5 is a flowchart showing an allocation amount calculation processof the allocation amount calculation unit according to the firstembodiment.

FIG. 6 is a functional block diagram of a communication system accordingto a second embodiment.

FIG. 7 is a functional block diagram of a communication system accordingto a third embodiment.

FIG. 8 is a diagram showing an example of results obtained by sweepprocessing according to the third embodiment.

FIG. 9 is a flowchart showing a processing latency estimation process ofa control parameter estimation unit according to the third embodiment.

FIG. 10 is a flowchart showing a process in which the control parameterestimation unit specifies a leading candidate cycle number according tothe third embodiment.

FIG. 11 is a first flowchart showing a minimum arrival amount estimationprocess of the control parameter estimation unit according to the thirdembodiment.

FIG. 12 is a second flowchart showing a minimum arrival amountestimation process of the control parameter estimation unit according tothe third embodiment.

FIG. 13 is a diagram showing an example of a traffic pattern and anoverview of a process of estimating the number of burst frames.

FIG. 14 is a diagram showing an example of a traffic pattern and anoverview of a process of estimating the number of burst frames.

FIG. 15 is a first flowchart showing a process in which a controlparameter estimation unit estimates the number of burst frames accordingto a fourth embodiment.

FIG. 16 is a second flowchart showing a process in which the controlparameter estimation unit estimates the number of burst frames accordingto the fourth embodiment.

FIG. 17 is a third flowchart showing a process in which the controlparameter estimation unit estimates the number of burst frames accordingto the fourth embodiment.

FIG. 18A is a diagram showing a relationship between atransmission-permitted period for an ONU and an arrival period of mobiledata according to a prior art.

FIG. 18B is a diagram showing a relationship between atransmission-permitted period for an ONU and an arrival period of mobiledata according to a prior art.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

An example in which a relay system which relays communication of amobile wireless communication system is a passive optical network (PON)will be described below. In a PON system, an optical line terminal (OLT)corresponds to terminal station device, and an optical network unit(ONU) corresponds to terminal device. The OLT is connected to aplurality of ONUs, and the plurality of ONUs transmit upstream data tothe OLT by time-division multiple access (TDMA). The OLT operates as abandwidth allocation device which allocates a transmission-permittedperiod start position and a bandwidth amount of upstream data to theONUs. The transmission-permitted period indicates a period in which anONU is permitted to transmit upstream data, and thetransmission-permitted period start position indicates the timing atwhich the transmission-permitted period begins.

The mobile wireless communication system includes an upper device, lowerdevices, and a user terminal. The user terminal is a communicationterminal that wirelessly communicates with the lower devices. In thecase of downstream communication, the upper device transmits downstreamuser data, which is downstream data addressed to the user terminal, tothe OLT, and the OLT broadcasts the downstream user data to subordinateONUs. Each ONU extracts downstream user data addressed to a subordinatelower device from the broadcast downstream user data and transmits theextracted downstream user data to the lower device. The lower devicewirelessly transmits the downstream user data to the user terminal. Inthe case of upstream communication, a lower device transmits mobiledata, which is upstream user data wirelessly received from the userterminal, to an ONU, and the ONU transmits the mobile data received fromthe lower device to the OLT according to a bandwidth allocation amount(hereinafter referred to as “allocation amount”) designated by the OLT.The OLT transmits the received mobile data to the upper device.

An OLT of the present embodiment estimates a start position and a lengthof a mobile data arrival period at every TTI of ONUs and determines atransmission-permitted period start position and a length of atransmission-permitted period of upstream data for each ONU on the basisof the estimation results. The OLT determines an allocation amount ofeach ONU on the basis of the determined transmission-permitted periodstart position and length of transmission-permitted period and notifieseach ONU of the determined allocation amount.

[Pre-Determination]

First, an allocation cycle length and a minimum arrival amount aredetermined in advance. An allocation cycle is a minimum unit of a periodtreated as a bandwidth allocation target by an OLT, and the allocationcycle length is a length (period) of one allocation cycle. The minimumarrival amount is a minimum value of the amount of data that can arriveat an ONU in the allocation cycle.

The allocation cycle length is a value obtained by dividing a TTI lengthinto a plurality of segments, and a value of (the allocation cyclelength×a division number) coincides with the TTI length. Also, theminimum arrival amount is the amount of mobile data which arrives at theONU per allocation cycle under the condition that a mobile data arrivalperiod, which is a period in which mobile data arrives at the ONU,becomes the longest. When the amount of data that can be transmitted inthe mobile data arrival period is D, the minimum arrival amount is avalue obtained by multiplying the data amount D and a value obtained bydividing the allocation cycle length by the mobile data arrival periodlength. That is, the minimum arrival amount is obtained by (data amountD×(allocation cycle length)/(mobile data arrival period length)). Also,when the minimum arrival amount is greater than a value A obtained bydividing the maximum amount of data that can be transmitted in theallocation cycle length by the number of ONUs, the obtained value A maybe the minimum arrival amount.

In the following descriptions and drawings, a case in which the divisionnumber is 8 is shown as an example, but the division number is notlimited thereto.

[Overview of all Processing]

In the present embodiment, an OLT separately performs a process ofestimating a start position of a mobile data arrival period regarding anONU and determining the estimated start position as atransmission-permitted period start position of upstream data regardingthe ONU and a process of estimating a length of the mobile data arrivalperiod regarding the ONU and determining the estimated length as alength of a transmission-permitted period for the ONU.

FIG. 1 is a diagram showing an example of a transmission-permittedperiod. In the process of determining a transmission-permitted periodstart position, as shown in FIG. 1, an OLT estimates a start position ofa mobile data arrival period regarding an ONU by adding a processinglatency of a lower device to a mobile data receiving time or a starttime of a TTI regarding the ONU as an offset. The estimated startposition becomes a transmission-permitted period start position. Here, amobile data receiving time regarding a lower device subordinate to theONU may be used as the mobile data receiving time regarding the ONU.Also, a time obtained by additionally adding a value in which atransmission delay is taken into consideration and the like to themobile data receiving time regarding the lower device may be treated asa mobile data receiving time.

In the process of determining a length of a transmission-permittedperiod, the OLT determines a transmission-permitted period on the basisof a minimum arrival amount which is the minimum amount of mobile datathat can arrive at the ONU in an allocation cycle. Specifically, thetransmission-permitted period is the period of the number of allocationcycles equal to a value obtained by dividing a mobile data amountspecified by radio resource information or a statistical processdescribed in a prior art by the minimum arrival amount (mobile dataamount/minimum arrival amount×allocation cycle length).

Since the transmission-permitted period is obtained by using the minimumamount basis as described above, it is possible to avoid a lack of atransmission-permitted period even when the gap between pieces of mobiledata is large and a mobile data arrival period is long. As a result, thetransmission-permitted period can include the entire arrival period ofupstream user data. Also, since a length of the transmission-permittedperiod is adaptively changed according to the amount of mobile data,bandwidth allocation can be optimized, and excessive bandwidthallocation is not continued.

First Embodiment

[OLT Configuration]

A first embodiment of the present invention will be described on thebasis of the above description. FIG. 2 is a functional block diagram ofa communication system 100 according to the first embodiment. Thecommunication system 100 includes an upper device 1, an OLT 2, an ONU 3,and a lower device 4. FIG. 2 shows one each of the upper device 1, theONU 3, and the lower device 4, but the communication system 100 caninclude a plurality of each. The number of ONUs 3 connected to the OLT 2is referred to as a connected ONU number.

The OLT 2 includes a cooperative processing unit 21, atransmission-permitted period start position determining unit 22, atransmission-permitted period length determining unit 23, an allocationamount calculation unit 24, and a transceiver unit 25. The cooperativeprocessing unit 21 receives radio resource information from the upperdevice 1 and specifies a mobile data receiving time and a mobile dataamount regarding the ONU 3 on the basis of the received radio resourceinformation. The cooperative processing unit 21 can perform thisprocessing by using the technology of Non-Patent Document 1. The radioresource information shows allocation of radio resources to each userterminal, and it is possible to acquire the amount of mobile data thatthe lower device 4 receives from each user terminal and a mobile datareceiving time of each piece of the mobile data on the basis of theallocated radio resources. The cooperative processing unit 21 calculatesa mobile data receiving time and a mobile data amount in each ONU 3 onthe basis of the mobile data receiving time and the mobile data amountof a lower device 4 subordinate to the ONU 3.

The transmission-permitted period start position determining unit 22determines a transmission-permitted period start position of the ONU 3on the basis of the mobile data receiving time regarding the ONU 3. Thetransmission-permitted period length determining unit 23 determines atransmission-permitted period length for each ONU 3 on the basis of themobile data amount of the ONU 3. The allocation amount calculation unit24 determines an allocation amount of each ONU 3 on the basis of thetransmission-permitted period start position determined by thetransmission-permitted period start position determining unit 22 and thetransmission-permitted period length determined by thetransmission-permitted period length determining unit 23 regarding eachONU 3. The transceiver unit 25 converts an electrical signalrepresenting downstream data received from the upper device 1 into anoptical signal and transmits the optical signal to the ONU 3. Thetransceiver unit 25 converts an optical signal representing upstreamdata received from an ONU 3 into an electrical signal and transmits theelectrical signal to the upper device 1. Also, the transceiver unit 25notifies the ONU 3 of the allocation amount of each allocation cycle.The process of the transceiver unit 25 is the same as that of a priorart.

In FIG. 2, the cooperative processing unit 21, thetransmission-permitted period start position determining unit 22, thetransmission-permitted period length determining unit 23, and theallocation amount calculation unit 24 are provided in the OLT 2, but allor some of them can be provided in a bandwidth allocation device whichis an external device of the OLT 2.

Details of the transmission-permitted period start position determiningunit 22, the transmission-permitted period length determining unit 23,and the allocation amount calculation unit 24 will be described below.

[Details of Transmission-Permitted Period Start Position DeterminingUnit 22]

When a start time of an allocation cycle treated as a bandwidthallocation target is received from the allocation amount calculationunit 24, the transmission-permitted period start position determiningunit 22 calculates a time by adding a processing latency of the lowerdevice 4 as an offset to a mobile data receiving time in the ONU 3obtained on the basis of the radio resource information. Thetransmission-permitted period start position determining unit 22acquires a time earlier than the start time of the allocation cycleamong calculated times from the cooperative processing unit 21 andoutputs the acquired time to the allocation amount calculation unit 24as a transmission-permitted period start position. In other words, theradio resource information which is treated as an acquisition targetfrom the cooperative processing unit 21 satisfies Equation (1) below.[Math. 1]Time[i]+T _(latency) ≤T _(alloc_start)

Time[i]≤T _(alloc_start) −T _(latency)   (1)

In Equation (1), Time[i] is a mobile data receiving time regarding ONU#i which is an i^(th) ONU 3. T_(latency) is a processing latency spentfor internal processing in the lower device 4, and T_(alloc_start) is astart time of an allocation cycle treated as a bandwidth allocationtarget. The transmission-permitted period start position determiningunit 22 treats a time obtained by subtracting the processing latencyT_(latency) from the start time T_(alloc_start) as a basis so thatEquation (1) is satisfied. The transmission-permitted period startposition determining unit 22 acquires radio resource informationindicating the mobile data receiving time Time[i] earlier than thevalue, which is treated as the basis, from the cooperative processingunit 21. Accordingly, the value acquired from the radio resourceinformation (the mobile data receiving time Time[i]) is a value beforeaddition of the processing latency. Therefore, thetransmission-permitted period start position determining unit 22outputs, as a transmission-permitted period start position of ONU #i, atime obtained by adding the processing latency T_(latency) to a value ofthe mobile data receiving time Time[i] of ONU #i acquired from the radioresource information.

The processing latency T_(latency) may be determined in advance on thebasis of a time spent for internal processing in each lower device 4.The transmission-permitted period start position determining unit 22 maydetermine the start time T_(alloc_start) on the basis of a delay (roundtrip time (RTT)) dependent on a transmission distance between the OLT 2and the ONU 3. In this case, the transmission-permitted period startposition determining unit 22 determines the start time T_(alloc_start)on the basis of Equation (2) instead of Equation (1). In Equation (2),T_(delay) represents a delay time dependent on the transmissiondistance.[Math. 2]Time[i]+T _(latency) +T _(delay) ≤T _(alloc_start)

Time[i]≤T _(alloc_start) −T _(latency) −T _(delay)   (2)

The transmission-permitted period length determining unit 23 is alsonotified of the radio resource information read from the cooperativeprocessing unit 21, and the radio resource information is eliminatedfrom the cooperative processing unit 21.

[Details of Transmission-Permitted Period Length Determining Unit 23]

The transmission-permitted period length determining unit 23 acquires amobile data amount of each ONU 3 from the radio resource informationread from the cooperative processing unit 21 according to an instructionfrom the transmission-permitted period start position determining unit22 and calculates a transmission-permitted period length. An equationfor calculating a transmission-permitted period length is given asEquation (3).

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 3} \rbrack & \; \\{{N_{cycle}\lbrack i\rbrack} = {\min( {N_{grant},\lceil \frac{{DataSize}\lbrack i\rbrack}{D_{m\; i\; n}} \rceil} )}} & (3)\end{matrix}$

In Equation (3), DataSize[i] is a mobile data amount of ONU #i,N_(cycle)[i] is the number of allocation cycles treated as atransmission-permitted period for ONU #i, D_(min) is a minimum arrivalamount, and N_(grant) is a division number of a TTI length (the numberof allocation cycles per TTI). The mobile data amount DataSize[i] thatcan arrive at ONU #i is calculated on the basis of the sum of mobiledata amounts in the lower device 4 subordinate to ONU #i. The mobiledata amount DataSize[i] represents the amount of mobile data to betransmitted from ONU #i to the OLT 2. When N_(cycle)[i] exceedsN_(grant), the transmission-permitted period length determining unit 23treats a value of the number of allocation cycles N_(cycle)[i] as thedivision number N_(grant) of the TTI length. That is, when a mobile dataamount exceeds the amount of data that can be transmitted in one TTI, atransmission-permitted period is determined to be the TTI length.

The transmission-permitted period length determining unit 23 outputsN_(cycle)[i] of each ONU #i to the allocation amount calculation unit 24as a transmission-permitted period length.

[Details of Allocation Amount Calculation Unit 24]

The allocation amount calculation unit 24 equally distributes abandwidth available in an allocation cycle among ONUs 3 whosetransmission-permitted periods are included in the allocation cycletreated as a bandwidth allocation target. Meanwhile, when atransmission-permitted period is not included in an allocation cycletreated as a bandwidth allocation target by all of ONUs 3, a bandwidthin the allocation cycle is equally distributed among all of the ONUs 3.The allocation amount calculation unit 24 performs this processing ateach allocation cycle treated as a bandwidth allocation target.

FIG. 3 is a flowchart showing a bandwidth allocation process of theallocation amount calculation unit 24. The allocation amount calculationunit 24 performs the flow shown in FIG. 3 from the beginning to the endevery time an allocation cycle treated as a bandwidth allocation targetis changed. First, the allocation amount calculation unit 24 acquires atransmission-permitted period start position of each ONU 3 updated onthe basis of a start time of the allocation cycle by thetransmission-permitted period start position determining unit 22. Also,the allocation amount calculation unit 24 acquires atransmission-permitted period for each ONU 3 from thetransmission-permitted period length determining unit 23 (step S10). Theallocation amount calculation unit 24 calculates an allocation amount ofeach ONU 3 on the basis of an updated transmission-permitted periodlength for each ONU 3 (step S20). The allocation amount calculation unit24 calculates a start time of the next allocation cycle (step S30).

FIG. 4 is a flowchart showing a transmission-permitted period startposition and transmission-permitted period length update process in stepS10 of FIG. 3. The allocation amount calculation unit 24 notifies thetransmission-permitted period start position determining unit 22 of astart time of an allocation cycle treated as a bandwidth allocationtarget and acquires a transmission-permitted period start position and atransmission-permitted period length from the transmission-permittedperiod start position determining unit 22 and the transmission-permittedperiod length determining unit 23, respectively.

Specifically, the allocation amount calculation unit 24 notifies thetransmission-permitted period start position determining unit 22 of astart time T_(alloc_start) of the allocation cycle treated as thebandwidth allocation target (step S105). The cooperative processing unit21 calculates a mobile data receiving time and a mobile data amount ofeach lower device 4 on the basis of radio resource information andcalculates a mobile data receiving time and a mobile data amount of eachONU 3 on the basis of mobile data receiving times and mobile dataamounts of each lower device 4 subordinate to the ONU 3. Thetransmission-permitted period start position determining unit 22acquires ONU #j (j is an integer greater than or equal to 1 and smallerthan or equal to a connected ONU number) whose mobile data receivingtime Time[j] is ahead of a time obtained by subtracting the processinglatency T_(latency) from the start time T_(alloc_start) with referenceto a mobile data receiving time of each ONU 3 calculated by thecooperative processing unit 21.

The transmission-permitted period start position determining unit 22calculates a transmission-permitted period start position by adding theprocessing latency T_(latency) to the acquired mobile data receivingtime Time[j] of ONU #j and notifies the allocation amount calculationunit 24 of the transmission-permitted period start position. Thetransmission-permitted period start position determining unit 22instructs the transmission-permitted period length determining unit 23to calculate a transmission-permitted period length N_(cycle)[j] of ONU#j. The transmission-permitted period length determining unit 23calculates the transmission-permitted period length N_(cycle)[j] of ONU#j as instructed by the transmission-permitted period start positiondetermining unit 22 through Equation (3) by using a mobile data amountDataSize[j] of ONU #j calculated by the cooperative processing unit 21.The transmission-permitted period length determining unit 23 notifiesthe allocation amount calculation unit 24 of the calculated number ofallocation cycles N_(cycle)[j] of ONU #j. When the allocation amountcalculation unit 24 acquires transmission-permitted period lengthsN_(cycle)[j] of all ONU #j (step S110), the allocation amountcalculation unit 24 performs processing from step S115 onward.

In step S115 to step S140, when a transmission-permitted period startposition and a transmission-permitted period length of each ONU 3 areacquired, the allocation amount calculation unit 24 adds an acquiredtransmission-permitted period to a transmission-permitted period holdingvalue for each ONU 3. At this time, the number of ONUs 3 whosetransmission-permitted period holding values are not 0 in a currentallocation cycle (the number of ONUs whose transmission-permittedperiods overlap) is measured as an effective ONU numberN_(onu_effective).

Specifically, the allocation amount calculation unit 24 initializes avariable i and the effective ONU number N_(onu_effective) by settingthem to 0 (step S115). The allocation amount calculation unit 24determines whether the variable i has reached the connected ONU number(step S120). When it is determined that the variable i has not reachedthe connected ONU number, the allocation amount calculation unit 24 addsa transmission-permitted period length N_(cycle)[i] to a currenttransmission-permitted period holding value N_(cycle_hold)[i] of ONU #i(step S125). When it is determined that the transmission-permittedperiod holding value N_(cycle_hold)[i] is greater than 0, the allocationamount calculation unit 24 adds 1 to a value of the currently effectiveONU number N_(onu_effective) (step S135). After it is determined in stepS130 that the transmission-permitted period holding valueN_(cycle_hold)[i] is smaller than or equal to 0, or after the processingof step S135, the allocation amount calculation unit 24 adds 1 to acurrent value of the variable i (step S140) and repeats the processingfrom step S120. When it is determined that the variable i has reachedthe connected ONU number, the allocation amount calculation unit 24finishes the processing of FIG. 4.

FIG. 5 is a flowchart showing allocation amount calculation processingin step S20 of FIG. 3.

Following the processing of FIG. 4, the allocation amount calculationunit 24 calculates an allocation amount of each ONU 3 in an allocationcycle of an allocation target. The relevant calculation includes twosteps of initially allocating a bandwidth part fixedly allocated to allthe ONUs 3 regardless of whether the relevant allocation cycle is atransmission-permitted period (fixed allocation processing) and thenadditionally allocating a remaining bandwidth to each ONU 3 adaptivelyaccording to whether the relevant allocation cycle is atransmission-permitted period (additional allocation processing).

In the fixed allocation processing of step S205 to step S225, theallocation amount calculation unit 24 allocates a bandwidth, which isfixedly allocated at each allocation cycle (a fixed allocation amountG_(fix)), to all the ONUs 3 connected to the OLT 2 as an allocationamount. For example, the fixed allocation amount is the amount of datacorresponding to a bandwidth required to transmit a control signal whichis sent between an upper device 1 and a lower device 4. An overheadamount and the like for burst transmission may be added to this fixedallocation amount on the basis of rules of an allocation amountnotification method in a TDM-PON.

Specifically, the allocation amount calculation unit 24 initializes thevariable i by setting it to 0 and initializes a non-allocated bandwidthamount by setting it to a bandwidth amount which is available in anallocation cycle (step S205). The allocation amount calculation unit 24determines whether the variable i has reached a connected ONU number(step S210). When it is determined that the variable i has not reachedthe connected ONU number, the allocation amount calculation unit 24treats an allocation amount Q[i] of ONU #i as the fixed allocationamount G_(fix) (step S215). The allocation amount calculation unit 24updates the non-allocated bandwidth amount with a value obtained bysubtracting the fixed allocation amount G_(fix) from the non-allocatedbandwidth amount (step S220). The allocation amount calculation unit 24adds 1 to the current value of the variable i (step S225) and repeatsthe processing from step S210. When it is determined that the variable ihas reached the connected ONU number, the allocation amount calculationunit 24 performs additional allocation processing from step S230.

In the additional allocation processing of step S230 to step S270, theallocation amount calculation unit 24 equally distributes a bandwidthwhich has not been allocated in an allocation cycle after the fixedallocation processing to ONUs 3 whose transmission-permitted periodholding values N_(cycle_hold)[i] calculated in step S10 are not 0. Anallocation amount corresponding to this equally distributed bandwidth(an additional allocation amount G_(add)) is given by Equation (4).

$\begin{matrix}{G_{add}\{ \begin{matrix}\lfloor \frac{G_{effective}}{N_{{onu}\;\_\;{effective}}} \rfloor & {{if},\mspace{11mu}{N_{{onu}\;\_\;{effective}} > 0}} \\{\lfloor \frac{G_{effective}}{N_{onu}} \rfloor,} & {otherwise}\end{matrix} } & (4)\end{matrix}$

In Equation (4), G_(effective) is a value obtained by extracting only abandwidth that can be used to transmit user data in the non-allocatedbandwidth. For example, G_(effective) is a value that can be obtained byexcluding a bandwidth of parity bits for error correction.N_(onu_effective) is the effective ONU number calculated in step S10,and N_(onu) is the connected ONU number, that is, the total number ofONUs 3 which are in connection with the OLT 2. When the effective ONUnumber is 0, the allocation amount calculation unit 24 adds theadditional allocation amount G_(add) to an allocation amount of all ofthe ONUs 3. When the effective ONU number is not 0, the allocationamount calculation unit 24 adds the additional allocation amount G_(add)to an allocation amount of only ONUs 3 whose transmission-permittedperiod holding values are not 0 and decreases the transmission-permittedperiod holding values.

Specifically, the allocation amount calculation unit 24 calculates theadditional allocation amount G_(add) by Equation (4) (step S230). Theallocation amount calculation unit 24 initializes the variable i bysetting it to 0 (step S235). The allocation amount calculation unit 24determines whether the variable i has reached the connected ONU number(step S240). When it is determined that the variable i has not reachedthe connected ONU number, the allocation amount calculation unit 24determines whether at least one condition is satisfied between(condition 1) that a transmission-permitted period holding valueN_(cycle_hold)[i] for ONU #i is greater than 0 and (condition 2) thatthe effective ONU number N_(onu_effective) is 0 (step S245). When it isdetermined that at least one of condition 1 and condition 2 issatisfied, the allocation amount calculation unit 24 adds the additionalallocation amount G_(add) to the current allocation amount Q[i] of ONU#i (step S250).

After it is determined that neither of condition 1 and condition 2 issatisfied in step S245, or after the processing of step S250, theallocation amount calculation unit 24 determines whether thetransmission-permitted period holding value N_(cycle_hold)[i] for ONU #iis greater than 0 (step S255). When it is determined that thetransmission-permitted period holding value N_(cycle_hold)[i] is greaterthan 0, the allocation amount calculation unit 24 subtracts 1 from acurrent value of the transmission-permitted period holding valueN_(cycle_hold)[i] (step S260). Meanwhile, when it is determined that thetransmission-permitted period holding value N_(cycle_hold)[i] for ONU #iis smaller than or equal to 0, the allocation amount calculation unit 24sets the transmission-permitted period holding value N_(cycle_hold)[i]to 0 (step S265). After the processing of step S260 or step S265, theallocation amount calculation unit 24 adds 1 to the current value of thevariable i (step S270) and repeats the processing from step S240. Whenit is determined that the variable i has reached the connected ONUnumber, the allocation amount calculation unit 24 finishes theprocessing of FIG. 5.

When the processing of FIG. 5 is finished, the allocation amountcalculation unit 24 performs the processing of step S30 of FIG. 3,outputs an allocation amount Q[i] of each ONU #i determined in the fixedallocation processing and the additional allocation processing of FIG. 5to the transceiver unit 25, and notifies each ONU 3 of the allocationamount Q[i].

The first embodiment of the present invention has been described above.In the additional allocation processing of the above description, whenan effective ONU number is 0, a non-allocated bandwidth is equallydivided by a connected ONU number, but the present invention is notlimited to this case. For example, the allocation amount calculationunit 24 may treat a non-allocated bandwidth as a bandwidth for detectinga new ONU. Also, the allocation amount calculation unit 24 may equallydistribute a non-allocated bandwidth to ONUs 3 whose mobile data amountsare 0.

Further, it has been described above that a transmission-permittedperiod start position and a transmission-permitted period length aredetermined at each allocation cycle, but a plurality of allocationcycles may be collectively processed. In this case, the allocationamount calculation unit 24 notifies the transmission-permitted periodstart position determining unit 22 of an end time of a period obtainedby collecting the plurality of allocation cycles and acquires atransmission-permitted period start position and atransmission-permitted period length corresponding to the end time. Theallocation amount calculation unit 24 temporarily holds the acquiredvalues and compares a start time of an allocation cycle, which is anexecution target of bandwidth allocation, and the heldtransmission-permitted period start position when performing bandwidthallocation of each allocation cycle in the collected period. When thetransmission-permitted period start position is earlier than the starttime of the allocation cycle which is the execution target of bandwidthallocation, the allocation amount calculation unit 24 adds thetransmission-permitted period length held in the allocation cycle to atransmission-permitted period holding value.

Second Embodiment

FIG. 6 is a functional block diagram of a communication system 101according to a second embodiment. In FIG. 6, parts identical to those ofthe communication system 100 according to the first embodiment shown inFIG. 2 are given the same reference numerals, and descriptions thereofare omitted. The communication system 101 shown in FIG. 6 differs fromthe communication system 100 shown in FIG. 2 in that an OLT 2 a isprovided instead of the OLT 2. The OLT 2 a differs from the OLT 2 shownin FIG. 2 in that a traffic monitoring unit 26 and a statisticalprocessing unit 27 are provided instead of the cooperative processingunit 21, and a transmission-permitted period start position determiningunit 22 a is provided instead of the transmission-permitted period startposition determining unit 22.

At each allocation cycle, the traffic monitoring unit 26 monitors thetraffic amount of upstream data transmitted from each ONU 3 in anallocation cycle. The traffic monitoring unit 26 notifies thestatistical processing unit 27 and the transmission-permitted periodstart position determining unit 22 a of a monitored value. Thestatistical processing unit 27 estimates a mobile data amount of eachONU 3 in each TTI from an upstream data amount of each ONU 3 acquiredfrom the traffic monitoring unit 26. For example, the method disclosedin Non-Patent Document 2 may be used as an estimation method.Specifically, an average μ and a variance σ of mobile data amounts ofrespective ONUs 3 in each TTI (per autonomous period which is describedbelow) are separately calculated from traffic monitoring values, andμ[i]+M×σ[i] (M is an integer) is treated as a mobile data amount of ONU#i.

The transmission-permitted period start position determining unit 22 adetects a time at which generation of mobile data begins in anautonomous period (whose period length is the same as a TTI length) fromresults acquired from the traffic monitoring unit 26. Specifically, thetransmission-permitted period start position determining unit 22 aacquires traffic monitoring results of each ONU 3 in each allocationcycle and observes, at each autonomous period, allocation cyclesswitching from an allocation cycle in which the amount of monitoringvalues of mobile data amounts indicated by the traffic monitoringresults is less than a threshold value to an allocation cycle in whichthe amount is the threshold value or more. When these switchingallocation cycles are detected, the transmission-permitted period startposition determining unit 22 a extracts a time difference between astart time of the detected allocation cycles and a start time of anautonomous cycle. In the second embodiment, the OLT 2 a performsallocation processing by treating a start time of an autonomous periodas a start time of a TTI. For this reason, the extracted time differenceis considered to be a processing latency from the view of the OLT 2 a.Therefore, the time difference is treated as a processing latency in thesecond embodiment and is held in the transmission-permitted period startposition determining unit 22 a. The threshold value is, for example, theamount of non-user data of a control signal and the like transmittedfrom a lower device 4 to an upper device 1. The autonomous period is aperiod controlled by the OLT 2 a and may or may not be synchronized witha TTI of a mobile wireless communication system.

When the transmission-permitted period start position determining unit22 a is notified of a start time of an allocation cycle, which istreated as a bandwidth allocation target, by the allocation amountcalculation unit 24, the transmission-permitted period start positiondetermining unit 22 a confirms whether the start time that is notifiedof is after a time obtained by adding the held value (the processinglatency) to the start time of the autonomous period as an offset. Whenthe start time of the allocation cycle is after the time calculatedthrough the addition, an instruction is issued to read the mobile dataamounts statistically obtained from the statistical processing unit 27.The transmission-permitted period length determining unit 23 is notifiedof the read mobile data amount of each ONU 3, and atransmission-permitted period length is determined by the sameprocessing as in the first embodiment.

In FIG. 6, the traffic monitoring unit 26, the statistical processingunit 27, the transmission-permitted period start position determiningunit 22 a, the transmission-permitted period length determining unit 23,and the allocation amount calculation unit 24 are provided in the OLT 2a, but all or some of them can be provided in a bandwidth allocationdevice which is an external device of the OLT 2 a.

Third Embodiment

FIG. 7 is a functional block diagram of a communication system 102according to a third embodiment. In FIG. 7, parts identical to those ofthe communication system 100 according to the first embodiment shown inFIG. 2 are given the same reference numerals, and descriptions thereofare omitted. The communication system 102 shown in FIG. 7 differs fromthe communication system 100 shown in FIG. 2 in that an OLT 2 b isprovided instead of the OLT 2. The OLT 2 b differs from the OLT 2 shownin FIG. 2 in that a control parameter estimation unit 28 is provided.The control parameter estimation unit 28 estimates a processing latencyT_(latency) in a lower device 4 and a minimum arrival amount D_(min)which is a minimum amount of upstream data transmitted from a lowerdevice 4 to an ONU 3.

The control parameter estimation unit 28 estimates the processinglatency T_(latency) and then estimates the minimum arrival amountD_(min). In these estimations, an accumulated data amount included in arequired transmission amount notification obtained from an ONU 3 isused. The accumulated data amount indicates the data amount ofnon-transmitted upstream data which should be transmitted to an upperdevice but is stored in the ONU 3 at a point in time at which therequired transmission amount notification is transmitted. To acquire theaccumulated data amount, the control parameter estimation unit 28notifies a transmission instruction of the required transmission amountnotification to the ONU 3 through the allocation amount calculation unit24 and the transceiver unit 25.

When the transmission instruction is received from the control parameterestimation unit 28, the allocation amount calculation unit 24additionally allocates a bandwidth in which the ONU 3 transmits therequired transmission amount notification to the OLT regarding bandwidthallocation to an allocation cycle for a notification of the receivedtransmission instruction. When additionally allocating a bandwidth, theallocation amount calculation unit 24 ensures the bandwidth bysubtracting a bandwidth used to transmit the required transmissionamount notification from a bandwidth G_(effective) that can be used totransmit user data. The allocation amount calculation unit 24 providesthe notification to the ONU 3 through the transceiver unit 25 so thatthe ONU 3 transmits the required transmission amount notification in theallocated bandwidth.

When the required transmission amount notification is received from theONU 3 in response to the transmission instruction, the transceiver unit25 notifies the control parameter estimation unit 28 of the accumulateddata amount included in the required transmission amount notificationand a signal representing completion of reception. Due to theabove-described operation of the allocation amount calculation unit 24and the transceiver unit 25, the control parameter estimation unit 28can acquire the required transmission amount notification in response tothe transmission instruction and control the timing of acquiring therequired transmission amount notification. A process in which thecontrol parameter estimation unit 28 estimates the processing latencyT_(latency) and the minimum arrival amount D_(min) by using theaccumulated data amount is sequentially described below.

[Processing Latency Estimation Process]

In an estimation process of the processing latency T_(latency), thecontrol parameter estimation unit 28 detects an allocation cycle numberwhich is highly likely to include a time at which mobile data begins toarrive at the OLT 2 (hereinafter, referred to as a mobile data arrivaltime). Specifically, the control parameter estimation unit 28 provides anotification of a transmission instruction of a required transmissionamount notification in a TTI in which a mobile data amount indicatingthe amount of upstream user data received from a communication terminalof each user by a lower device is not 0. The control parameterestimation unit 28 switches allocation cycles for providing anotification of a transmission instruction of a required transmissionamount notification in numerical order. Hereinafter, the process ofproviding a notification of a transmission instruction while switchingallocation cycles in numerical order is referred to as sweep processing.

The control parameter estimation unit 28 acquires the number of timesthat an accumulated data amount greater than the threshold value isacquired in each allocation cycle while repeating sweep processing thecertain number of times. Hereinafter, the number of times that anaccumulated data amount greater than the threshold value is acquired isreferred to as a detection number. The control parameter estimation unit28 specifies a period in which allocation cycles with a detection numberof 0 continue and detects an allocation cycle with the highest detectionnumber after the specified period. The control parameter estimation unit28 estimates the detected allocation cycle as an allocation cycleincluding a mobile data arrival time. The control parameter estimationunit 28 calculates the processing latency T_(latency) by multiplying anallocation cycle length and a difference between the estimatedallocation cycle number and an allocation cycle number including amobile data receiving time.

FIG. 8 is a diagram showing an example of results obtained by sweepprocessing according to the third embodiment. FIG. 8 shows detectionnumbers in respective allocation cycles with allocation cycle numbers of0 to N_(grant)−1. In this example, a detection number of 0 continues ina period from an allocation cycle number of 0 to an allocation cyclenumber of 14 and a period from an allocation cycle number of 20 to anallocation cycle number of N_(grant)−1. Since a detection number of the16^(th) allocation cycle behind 0^(th) to 14^(th) allocation cycles isthe largest number, the control parameter estimation unit 28 estimatesthe 16^(th) allocation cycle as an allocation cycle including a mobiledata arrival time.

The range of allocation cycle numbers which are targets of sweepprocessing is determined as follows. An allocation cycle number of anallocation cycle with a start time closest to a time(Time[i]+T_(offset)) obtained by adding a predetermined offset timeT_(offset) to a mobile data receiving time (Time[i]) in a lower device 4connected to an i^(th) ONU 3 is treated as M_(receive)[i]. When theallocation cycle number M_(receive)[i] is used, the range of allocationcycle numbers which are targets of sweep processing is the range of S[i]satisfying Equation (5).

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 5} \rbrack & \; \\\{ \begin{matrix}{{{M_{receive}\lbrack i\rbrack} - K} \leq {S\lbrack i\rbrack} \leq {{M_{recieve}\lbrack i\rbrack} + K}} \\( {{{if}\mspace{14mu} K} \leq {M_{recieve}\lbrack i\rbrack} \leq {N_{grant} - K - 1}} ) \\{{{{M_{recieve}\lbrack i\rbrack} - K} \leq {S\lbrack i\rbrack} \leq {N_{grant} - 1}},} \\{0 \leq {S\lbrack i\rbrack} \leq {( {{M_{recieve}\lbrack i\rbrack} + K} ){mod}\; N_{grant}}} \\( {{{if}\mspace{14mu}{M_{recieve}\lbrack i\rbrack}} \geq {K\mspace{14mu}{and}\mspace{14mu}{M_{recieve}\lbrack i\rbrack}} > {N_{grant} - K - 1}} ) \\{{0 \leq {S\lbrack i\rbrack} \leq {{M_{recieve}\lbrack i\rbrack} + K}},} \\{{N_{grant} - 1 - K + {M_{recieve}\lbrack i\rbrack}} \leq {S\lbrack i\rbrack} \leq {N_{grant} - 1}} \\( {{{if}\mspace{14mu}{M_{recieve}\lbrack i\rbrack}} < {K\mspace{14mu}{and}\mspace{14mu}{M_{recieve}\lbrack i\rbrack}} \leq {N_{grant} - K - 1}} )\end{matrix}  & (5)\end{matrix}$

In Equation (5), S[i] indicates an allocation cycle number of anexamination target on which sweep processing is performed with respectto the i^(th) ONU 3. K is a value satisfying Equation (6). K is a valuefor determining how many allocation cycles are treated as examinationtargets centering on the allocation cycle number M_(receive)[i].

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 6} \rbrack & \; \\{0 < K \leq \lfloor \frac{N_{grant} - 1}{2} \rfloor} & (6)\end{matrix}$

FIG. 9 is a flowchart showing a processing latency estimation process ofthe control parameter estimation unit 28 according to the thirdembodiment. The control parameter estimation unit 28 executes the flowshown in FIG. 9 for each ONU 3 connected to the OLT 2 b. FIG. 9 showsprocessing for an i^(th) ONU 3 among connected ONUs 3. Hereinafter, thei^(th) ONU 3 is referred to as ONU #i.

When a process of estimating a processing latency begins, the controlparameter estimation unit 28 waits until a mobile data amountDataSize[i] and a mobile data receiving time Time[i] relating to ONU #iare newly acquired from the cooperative processing unit 21 (step S302).When a new mobile data amount and mobile data receiving time areacquired (step S302, YES), the control parameter estimation unit 28determines whether an under-estimation flag F[i], which indicates that aprocessing latency for ONU #i is being estimated, is 0 (step S304). Themobile data amount and the mobile data receiving time acquired from thecooperative processing unit 21 by the control parameter estimation unit28 are the same as those pieces of information acquired from thecooperative processing unit 21 by the transmission-permitted periodstart position determining unit 22. The control parameter estimationunit 28 may operate in synchronization with the transmission-permittedperiod start position determining unit 22.

When the under-estimation flag F[i] is 0 (step S304, YES), the controlparameter estimation unit 28 determines whether the acquired mobile dataamount DataSize[i] is greater than 0 (step S306). When the mobile dataamount is 0 (step S306, NO), the control parameter estimation unit 28returns the process to step S302. When the mobile data amount is greaterthan 0 (step S306, YES), the control parameter estimation unit 28 setsthe under-estimation flag F[i] to 1 which represents that the estimationis underway. Further, the control parameter estimation unit 28 specifiesthe allocation cycle number M_(receive)[i] on the basis of the acquiredmobile data receiving time (step S308).

The control parameter estimation unit 28 specifies the range ofallocation cycle numbers which are targets of sweep processing and setsS[i] to an allocation cycle number positioned at the front end of thespecified range (step S310). The allocation cycle indicated by S[i]initially becomes a target of examination. The control parameterestimation unit 28 outputs the allocation cycle number indicated by S[i]and a transmission instruction of a required transmission amountnotification to the allocation amount calculation unit 24 in order toacquire a required transmission amount notification in the allocationcycle indicated by S[i] (step S312) and returns the process to stepS302.

When the under-estimation flag F[i] is not 0 (step S304, NO), thecontrol parameter estimation unit 28 determines whether the transceiverunit 25 has received a required transmission amount notification inresponse to the transmission instruction of step S312 (step S314). Whenthe transceiver unit 25 has not received a required transmission amountnotification (step S314, NO), the control parameter estimation unit 28returns the process to step S302 and waits until the transceiver unit 25receives a required transmission amount notification. The transceiverunit 25 notifies completion of reception of a required transmissionamount notification to the control parameter estimation unit 28.Further, the control parameter estimation unit 28 is also notified of anaccumulated data amount included in the required transmission amountnotification.

When the transceiver unit 25 receives a required transmission amountnotification (step S314, YES), the control parameter estimation unit 28determines whether the accumulated data amount in ONU #i is greater thanor equal to the threshold value (step S316). When the accumulated dataamount is greater than or equal to the threshold value (step S316, YES),the control parameter estimation unit 28 determines that mobile data tobe transmitted in the allocation cycle which is an examination targetindicated by S[i] has been detected and increases a detection numberR[i][S[i]] by 1 (step S318). An initial value of each detection numberR[i][S[i]] is 0. When the accumulated data amount is less than thethreshold value (step S316, NO), the control parameter estimation unit28 advances the process to step S320. The threshold value is determinedin advance on the basis of, for example, the data amount of non-userdata of a control signal and the like transmitted from a lower device toan upper device. In step S316, it is determined whether upstream userdata (mobile data) is in data buffered in ONU #i.

The control parameter estimation unit 28 determines whether the acquiredmobile data amount is greater than 0 (step S320). When the mobile dataamount is smaller than or equal to 0 (step S320, NO), the controlparameter estimation unit 28 returns the process to step S302.

When the mobile data amount is greater 0 (step S320, YES), the controlparameter estimation unit 28 changes S[i] indicating the allocationcycle which is the current examination target with an allocation cyclenumber of an allocation cycle of the next examination target andincreases an examination cycle number R_(total)[i] by 1 (step S322). Thecontrol parameter estimation unit 28 determines whether the examinationcycle number R_(total)[i] is greater than a specified value (2K×L) (stepS324). When the examination cycle number R_(total)[i] is small than orequal to (2K×L) (step S324, NO), the control parameter estimation unit28 returns the process to step S312 in order to acquire a requiredtransmission amount notification of an allocation cycle which is thenext examination target indicated by S[i] changed in step S322.

The specified value (2K×L) in step S324 is the number of repetitions ofthe processing from step S302 to step S322. In other words, the controlparameter estimation unit 28 determines L times whether upstream userdata (mobile data) is in each of 2K allocation cycles which are targetsof sweep processing. The repetition number L is determined in advanceaccording to accuracy required for the processing latency.

When the examination cycle number R_(total)[i] is greater than (2K×L)(step S324, YES), the control parameter estimation unit 28 finishes thesweep processing and specifies, as a leading candidate cycle number, anallocation cycle number of an allocation cycle immediately after aperiod in which allocation cycles with a detection number of 0 continueon the basis of detection numbers R[i][S[i]] of respective allocationcycles (step S326). The leading candidate cycle, number indicates acandidate for an allocation cycle including a mobile data arrival time.

The control parameter estimation unit 28 specifies an allocation cyclewith the highest detection number R[i] among allocation cycles close toY from the allocation cycle indicated by the leading candidate cyclenumber as an allocation cycle number S_(lock)[i] of an allocation cycleincluding a mobile data arrival time (step S328). The value Ydetermining allocation cycles close to Y may be, for example, a valueobtained by multiplying a division number N_(grant) and ¼ or ⅛.

The control parameter estimation unit 28 calculates a processing latencyT_(latency) in a lower device 4 connected to ONU #i on the basis of theallocation cycle number S_(lock)[i] specified in step S328 and theallocation cycle number M_(receive)[i] (step S330) and finishes theestimation processing. The control parameter estimation unit 28calculates the processing latency T_(latency) by using Equation (7). InEquation (7), T_(period) is an allocation cycle length.

$\begin{matrix}{\mspace{79mu}\lbrack {{Math}.\mspace{14mu} 7} \rbrack} & \; \\{T_{latency} = \{ \begin{matrix}{{( {N_{grant} - {M_{recieve}\lbrack i\rbrack} + {S_{lock}\lbrack i\rbrack}} ) \times T_{period}},} & \begin{matrix}{{{if}\mspace{14mu}{M_{recieve}\lbrack i\rbrack}} -} \\{{S_{lock}\lbrack i\rbrack} > K}\end{matrix} \\{{( {{S_{lock}\lbrack i\rbrack} - {M_{recieve}\lbrack i\rbrack}} ) \times T_{period}},} & \begin{matrix}{{{if}\mspace{14mu} 0} < {{M_{recieve}\lbrack i\rbrack} -}} \\{{S_{lock}\lbrack i\rbrack} \leq K}\end{matrix} \\{{( {{S_{lock}\lbrack i\rbrack} - {M_{recieve}\lbrack i\rbrack}} ) \times T_{period}},} & \begin{matrix}{{{if}\mspace{14mu} 0} < {{S_{lock}\lbrack i\rbrack} -}} \\{{M_{recieve}\lbrack i\rbrack} \leq K}\end{matrix} \\{{( {{S_{lock}\lbrack i\rbrack} - N_{grant} - {M_{recieve}\lbrack i\rbrack}} ) \times T_{period}},} & \begin{matrix}{{{if}\mspace{14mu}{S_{lock}\lbrack i\rbrack}} -} \\{{M_{recieve}\lbrack i\rbrack} > K}\end{matrix}\end{matrix} } & (7)\end{matrix}$

FIG. 10 is a flowchart showing a process in which the control parameterestimation unit 28 specifies a leading candidate cycle number accordingto the third embodiment. The process shown in FIG. 10 shows an exampleof the processing of step S326 in the processing latency estimationprocess shown in FIG. 9. When the specification of a leading candidatecycle number begins, the control parameter estimation unit. 28initializes each variable used in the process (step S342).

In the initialization of variables, the control parameter estimationunit 28 sets a variable G to a first allocation cycle number in therange of allocation cycle numbers which are targets of sweeping, sets aconsecutive idle number and a maximum consecutive idle number to 0, andsets a leading candidate cycle number to the allocation cycle numberM_(receive)[i].

The control parameter estimation unit 28 determines whether theprocessing from step S346 to step S354 has been performed on all theallocation cycles which are targets of sweeping (step S344). When thereis an allocation cycle on which the processing has not been performed(step S344, NO), the control parameter estimation unit 28 determineswhether a detection number R[i][G] is greater than 0 (step S346).

When the detection number R[i][G] is smaller than or equal to 0 (stepS346, NO), the control parameter estimation unit 28 increases theconsecutive idle number by 1 (step S348) and advances the process tostep S356. When the detection number R[i][G] is greater than 0 (stepS346, YES), the control parameter estimation unit 28 determines whetherthe consecutive idle number is greater than the maximum consecutive idlenumber (step S350).

When the consecutive idle number is greater than the maximum consecutiveidle number (step S350, YES), the control parameter estimation unit 28treats the consecutive idle number as a new maximum consecutive idlenumber and updates the leading candidate cycle number with a currentvalue of G (step S352). When the consecutive idle number is smaller thanor equal to the maximum consecutive idle number (step S350, NO), thecontrol parameter estimation unit 28 advances the process to step S354.

The control parameter estimation unit 28 sets the consecutive idlenumber to 0 (step S354), increases the variable G indicating anallocation cycle number of a processing target by 1 (step S356), andreturns the process to step S344. When the above-described processingfrom step S344 to step S356 is performed on all the allocation cycleswhich are targets of sweeping (step S344, YES), the control parameterestimation unit 28 finishes the process of specifying a leadingcandidate cycle number.

The control parameter estimation unit 28 estimates the processinglatency T_(latency) according to the above flows shown in FIG. 9 andFIG. 10.

[Minimum Arrival Amount Estimation Process]

When the processing latency estimation process is complete, the controlparameter estimation unit 28 executes an estimation process of theminimum arrival amount D_(min) and successively updates an estimatedvalue of the minimum arrival amount D_(min). An initial value(D_(min,init)) of the minimum arrival amount D_(min) is given by, forexample, Equation (8). DataSize_(min) in Equation (8) is a minimum valuethat the mobile data amount DataSize[i] can have.

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 8} \rbrack & \; \\{D_{{m\; i\; n},{init}} = \lfloor \frac{{DataSize}_{m\; i\; n}}{N_{grant}} \rfloor} & (8)\end{matrix}$

In a certain number of allocation cycles after the allocation cycleindicated by S_(lock)[i], the control parameter estimation unit 28acquires a change in the accumulated data amount of ONU #i and estimatesa minimum arrival amount on the basis of the acquired change amount.When P indicates an allocation cycle number used to estimate a minimumarrival amount, the range of allocation cycles used for the estimationis from S_(lock)[i] to ((S_(lock)[i]+P) mod N_(grant)). The allocationcycle number P is greater than or equal to 1 and smaller than or equalto N_(grant).

FIG. 11 and FIG. 12 are flowcharts showing a minimum arrival amountestimation process of the control parameter estimation unit 28 accordingto the third embodiment. When a minimum arrival amount estimationprocess begins, the control parameter estimation unit 28 sets a variableJ to −1 (step S362) and waits until a mobile data amount DataSize[i] anda mobile data receiving time Time[i] relating to ONU #i are newlyacquired from the cooperative processing unit 21 (step S364). When newmobile data amount and mobile data receiving time are acquired (stepS364, YES), the control parameter estimation unit 28 determines whetherthe variable J is −1 (step S366).

When the variable J is −1 (step S366, YES), the control parameterestimation unit 28 determines whether a mobile data amount is greaterthan 0 (step S368). When the mobile data amount is smaller than or equalto 0 (step S368, NO), the control parameter estimation unit 28 returnsto process to step S364 and waits until a mobile data amount greaterthan 0 is acquired. When the mobile data amount is greater than 0 (stepS368, YES), the control parameter estimation unit 28 sets S[i] toS_(lock)[i] indicating an allocation cycle number of an allocation cycleincluding a mobile data arrival time and sets the variable J to 1 (stepS370).

In order to acquire a required transmission amount notification in anallocation cycle indicated by S[i], the control parameter estimationunit 28 outputs the allocation cycle number indicated by S[i] and atransmission instruction of a required transmission amount notificationto the allocation amount calculation unit 24 (step S372). Afteroutputting S[i] and the transmission instruction, the control parameterestimation unit 28 returns the process to step S364.

When the variable J is not −1 in step S366 (step S366, NO), the controlparameter estimation unit 28 determines whether output of thetransmission instruction of a required transmission amount notificationhas been finished (step S374). When the transmission of the transmissioninstruction has not been finished (step S374, NO), the control parameterestimation unit 28 advances the process to step S398. When thetransmission of the transmission instruction has been finished (stepS374, YES), the control parameter estimation unit 28 determines whetherthe transceiver unit 25 has received a required transmission amountnotification (step S376). When the transceiver unit 25 has not receiveda required transmission amount notification (step S376, NO), the controlparameter estimation unit 28 returns the process to step S364 and waitsuntil a mobile data amount and a mobile data receiving time relating toONU #i are newly acquired from the cooperative processing unit 21.

When the transceiver unit 25 has received a required transmission amountnotification (step S376, YES), the control parameter estimation unit 28determines whether the variable J is 0 (step S378). When the variable Jis 0 (step S378, YES), the control parameter estimation unit 28 sets adata amount D_(previous)[i] to an accumulated data amount included inthe required transmission amount notification (step S380) and advancesthe process to step S392.

When the variable J is not 0 (step S378, NO), the control parameterestimation unit 28 sets the data amount D_(previous)[i] to anaccumulated data amount (step S382) and calculates a data amountD_(est)[i] which has arrived at the OLT 2 b in the allocation cycleindicated by S[i] with Equation (9) (step S384).

$\begin{matrix}{\mspace{76mu}\lbrack {{Math}.\mspace{14mu} 9} \rbrack} & \; \\{{D_{est}\lbrack i\rbrack} = \{ \begin{matrix}{{{D_{current}\lbrack i\rbrack} - {D_{previous}\lbrack i\rbrack}},} & {{{if}\mspace{14mu}{D_{current}\lbrack i\rbrack}} \geq {D_{previous}\lbrack i\rbrack}} \\{{{D_{current}\lbrack i\rbrack} - {D_{previous}\lbrack i\rbrack} + \lfloor \frac{G_{effective}}{N_{grant}} \rfloor},} & {otherwise}\end{matrix} } & (9)\end{matrix}$

D_(current)[i] is an accumulated data amount of the allocation cycleindicated by the allocation cycle number S[i], and D_(previous)[i] is anaccumulated data amount of an allocation cycle indicated by anallocation cycle number (S[i]−1). When the accumulated data amount isreduced, the control parameter estimation unit 28 calculates thedifference as an arrived data amount. When the accumulated data amountis increased, the control parameter estimation unit 28 calculates anarrived data amount value by adding the difference to a value obtainedby dividing a bandwidth G_(effective) that can be used to transmit userdata by the division number N_(grant).

The control parameter estimation unit 28 determines whether thecalculated data amount D_(est)[i] is greater than the minimum arrivalamount D_(min) (step S386). When D_(est)[i] is greater than D_(min)(step S386, YES), the control parameter estimation unit 28 updatesD_(min) with a value of D_(est)[i] (step S388). When D_(est)[i] issmaller than or equal to D_(min) (step S386, NO), the control parameterestimation unit 28 advances the process to step S390. The controlparameter estimation unit 28 updates D_(previous)[i] with a value ofD_(current)[i] (step S390) and advances the process to step S392.

An upper limit of the minimum arrival amount D_(min) may be determined.An upper limit value D_(min_limit) of the minimum arrival amount D_(min)is determined in advance. When the upper limit of the minimum arrivalamount D_(min) is determined, D_(min) is updated by Equation (10) instep S388.[Math. 10]D _(min)=min(D _(min_limit) ,D _(est))  (10)

The control parameter estimation unit 28 increases the variable J by 1(step S392) and determines whether the variable J is greater than theallocation cycle number P (step S394). When the variable J is greaterthan P (step S394, YES), the control parameter estimation unit 28 setsthe variable J to 0 (step S396). When the variable J is smaller than orequal to P (step S394, NO), the control parameter estimation unit 28advances the process to step S398.

The control parameter estimation unit 28 determines whether the mobiledata amount DataSize[i] is greater than 0 (step S398) and returns theprocess to step S364 when DataSize[i] is smaller than or equal to 0(step S398, NO). When DataSize[i] is greater than 0 (step S398, YES),the control parameter estimation unit 28 updates S[i] by setting S[i] toa value indicated by (S_(lock)[i]+J) (step $400) and changes theallocation cycle which is the processing target with the next allocationcycle. The control parameter estimation unit 28 advances the process tostep S372 in order to acquire a required transmission amountnotification in an allocation cycle indicated by the updated S[i].

The control parameter estimation unit 28 performs each part ofprocessing from step S364 to step S400 on each allocation cycle fromS_(lock)[i] to ((S_(lock)[i]+P) mod N_(grant)) to estimate the minimumarrival amount D_(min). The control parameter estimation unit 28continuously performs the minimum arrival amount estimation processshown in FIG. 11 and FIG. 12.

In the OLT 2 b according to the third embodiment, the control parameterestimation unit 28 estimates a processing latency of a lower device 4 onthe basis of an accumulated data amount in an ONU 3. Further, thetransmission-permitted period start position determining unit 22determines a transmission-permitted period start position for the ONU 3on the basis of the estimated processing latency and a mobile datareceiving time. The OLT 2 b can accurately determine atransmission-permitted period including the entire arrival period ofmobile data by using the processing latency based on operation of theONU 3.

In the above description, the examination cycle number R_(total)[i] isused as a counter whose value is increased every time the value of S[i]is changed, but the timing of change is not limited thereto. Forexample, the control parameter estimation unit 28 may increase theexamination cycle number R_(total)[i] when an accumulated data amountincluded in a required transmission amount notification is greater thanor equal to the threshold value and the value of S[i] is updated. Inthis case, the total sum of detection numbers R[i] in respectiveallocation cycles which are targets of sweep processing is the samevalue as the examination cycle number R_(total)[i].

Fourth Embodiment

An OLT in a fourth embodiment performs traffic pattern estimation inaddition to the operation of the OLT 2 b in the third embodiment. Atraffic pattern is determined with the number of mobile data groups(burst data) which arrive at the OLT in one TTI. In the first to thirdembodiments, a case in which mobile data arrives at an OLT as one groupof consecutive data has been described. In the fourth embodiment, a casein which mobile data in one TTI is divided into one or more pieces ofburst data and arrives at an OLT is described.

In the fourth embodiment, an OLT has the same configuration as the OLT 2b of the third embodiment. In the fourth embodiment, the controlparameter estimation unit 28 estimates the number of mobile data groupstransmitted in one TTI (hereinafter, referred to as the number of burstframes) from a traffic pattern and determines K corresponding to thenumber of burst frames. The transmission-permitted period start positiondetermining unit 22 and the transmission-permitted period lengthdetermining unit 23 respectively determine a transmission-permittedperiod start position and a transmission-permitted period lengthaccording to the number of burst frames. K is a value for determininghow many allocation cycles are treated as examination targets centeringon an allocation cycle number M_(receive)[i]. In the fourth embodiment,K depends on the number of burst frames B, which is the number of mobiledata groups arriving in each TTI in a burst manner, and is determined byEquation (11).

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 11} \rbrack & \; \\{K = \lceil {\lfloor \frac{N_{grant} - 1}{2} \rfloor/B} \rceil} & (11)\end{matrix}$

FIG. 13 and FIG. 14 are diagrams showing examples of traffic patternsand overviews of processes of estimating the number of burst frames.FIG. 13 shows a traffic pattern in which mobile data intensively arrivesas one piece of burst data in each TI. In the traffic pattern shown inFIG. 13, the number of burst frames B is 1. FIG. 14 shows a trafficpattern in which mobile data is divided into two pieces of burst dataand arrives in each TTI. In the traffic pattern shown in FIG. 14, thenumber of burst frames B is 2. The number of burst frames B estimated inthe fourth embodiment is not a parameter changed depending on a mobiledata amount but is a static parameter determined depending oninstallation and the like of a lower device. Operation of the controlparameter estimation unit 28, the transmission-permitted period startposition determining unit 22, and the transmission-permitted periodlength determining unit 23 in the fourth embodiment is described below.

[Operation of Control Parameter Estimation Unit 28]

After estimating the number of burst frames, the control parameterestimation unit 28 estimates a processing latency T_(latency) and aminimum arrival amount D_(min) on the basis of K corresponding to theestimated number of burst frames. The process of estimating a processinglatency and a minimum arrival amount is the same as the processdescribed in the third embodiment. The control parameter estimation unit28 notifies the estimated number of burst frames, processing latency,and minimum arrival amount to the transmission-permitted period startposition determining unit 22 and the transmission-permitted periodlength determining unit 23.

The overview of a process in which the control parameter estimation unit28 estimates the number of burst frames is described with reference toFIG. 13 and FIG. 14. The control parameter estimation unit 28 dividesallocation cycles in one TTI into a first half allocation cycle and asecond half allocation cycle. In the example shown in FIG. 13, due tothe first division, the first half allocation cycle includes allocationcycles of allocation cycle numbers 0, 1, 2, and 3, and the second halfallocation cycle includes allocation cycles of allocation cycle numbers4, 5, 6, and 7. The control parameter estimation unit 28 compares thesum of detection numbers R in the first half allocation cycle and thesum of detection numbers in the second half allocation cycle.

In the example shown in FIG. 13, detection numbers R of the allocationcycles of allocation cycle numbers 0, 1, and 2 are 10 each, anddetection numbers R of the other allocation cycles are 0. Therefore, itis possible to obtain the sum of detection numbers in the first halfcycles (TS_(lower)[0]=30) and the sum of detection numbers in the secondhalf cycles (TS_(upper)[0]=0). When a difference between TS_(lower)[0]and TS_(upper)[0] is a certain value or more, the control parameterestimation unit 28 determines that the allocation of mobile data in therespective allocation cycles is biased. When a bias of allocation isdetected due to the first division, the control parameter estimationunit 28 determines that the number of burst frames is 1 (=2^((a-1)),a=1).

In the example shown in FIG. 14, detection numbers R of the allocationcycles of allocation cycle numbers 0, 1, 4, and 5 are 10 each, anddetection numbers R of the other allocation cycles are 0. Therefore, itis possible to obtain the sum of detection numbers in the first halfcycle (TS_(lower)[0]=20) and the sum of detection numbers in the secondhalf cycle (TS_(upper)[0]=20). When TS_(lower)[0] coincides withTS_(upper)[0] or a difference therebetween is not the certain value ormore, the control parameter estimation unit 28 further halves the firsthalf or second half cycle obtained by the first division. When thesecond half cycle obtained by the first division is halved, theallocation cycles of the allocation cycle numbers 4 and 5 are includedin a first half cycle, and the allocation cycles of the allocation cyclenumbers 6 and 7 are included in a second half cycle.

Due to the second division, it is possible to obtain the sum ofdetection numbers in the first half cycle (TS_(lower)[1]=20) and the sumof detection numbers in the second half cycle (TS_(upper)[1]=0). When adifference between TS_(lower)[1] and TS_(upper)[1] is the certain valueor more, the control parameter estimation unit 28 determines that theallocation of mobile data in the respective allocation cycles is biased.When a bias of allocation is detected due to the second division, thecontrol parameter estimation unit 28 determines that the number of burstframes is 2 (=2^((a-1)), a=2).

The control parameter estimation unit 28 recursively divides a TTIlength into a first half allocation cycle and a second half allocationcycle and detects a bias of mobile data amount allocated to the firsthalf allocation cycle and the second half allocation cycle. The controlparameter estimation unit 28 calculates an estimation value of thenumber of burst frames from the number of times of division performeduntil a bias of mobile data amount is detected.

The control parameter estimation unit 28 sweeps allocation cycle numbers0 to (N_(grant)−1), which indicate examination target allocation cyclesin order to sequentially switch allocation cycles, in order to detect anallocation cycle in which an accumulated data amount greater than apredetermined threshold value is received by treating all allocationcycles as examination targets. In this detection, K is given by Equation(12). The control parameter estimation unit 28 acquires a detectionnumber in each allocation cycle by repeating sweeping of allocationcycle numbers a certain number of times. A process of acquiring adetection number in each allocation cycle is the same as the processfrom step S302 to step S324 shown in FIG. 9 according to the thirdembodiment.

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 12} \rbrack & \; \\{K = \lfloor \frac{N_{grant} - 1}{2} \rfloor} & (12)\end{matrix}$

When a detection number in each allocation cycle is acquired, thecontrol parameter estimation unit 28 estimates the number of burstframes. FIG. 15, FIG. 16, and FIG. 17 are flowcharts showing a processin which the control parameter estimation unit 28 estimates the numberof burst frames according to the fourth embodiment. When estimation ofthe number of burst frames begins, the control parameter estimation unit28 sets three division points N_(div)[0], N_(div)[1], and N_(div)[2] asshown in Equation (13) (step S412).

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 13} \rbrack & \; \\\{ \begin{matrix}{{N_{div}\lbrack 0\rbrack} = {( {{M_{recieve}\lbrack i\rbrack} + {N_{grant}/4}} ){mod}\; N_{grant}}} \\{{N_{div}\lbrack 1\rbrack} = {( {{M_{recieve}\lbrack i\rbrack} + {N_{grant}/2}} ){mod}\; N_{grant}}} \\{{N_{div}\lbrack 2\rbrack} = {( {{M_{recieve}\lbrack i\rbrack} + {3 \cdot {N_{grant}/4}}} ){mod}\; N_{grant}}}\end{matrix}  & (13)\end{matrix}$

The control parameter estimation unit 28 clears each of burst occurrencenumbers U[0], U[1], . . . , and U[A] to 0 and sets a variable hindicting a repetition number to 0 (step S414). A indicates a candidatenumber for the number of burst frames. The control parameter estimationunit 28 determines whether h is greater than or equal to 3 (step S416).When h is smaller than 3 (step S416, NO), the control parameterestimation unit 28 clears detection number counters TS_(upper)[i] andTS_(lower)[i] (i=0, 1, . . . , and A−1) to 0 and set variables a and fto 0 (step S418).

The control parameter estimation unit 28 determines whether a divisionpoint N_(div)[h] is smaller than (N_(grant)/2) (step S420). When thedivision point N_(div)[h] is smaller than (N_(grant)/2) (step S420,YES), the control parameter estimation unit 28 sets ProbePos indicatingan allocation cycle number of an examination target allocation cycle to(N_(grant)−(N_(grant)/2−N_(div)[h])) (step S422). When the divisionpoint N_(div)[h] is greater than or equal to (N_(grant)/2) (step S420,NO), the control parameter estimation unit 28 sets ProbePos to(N_(div)[h]−N_(grant)/2) (step S424).

The control parameter estimation unit 28 determines whether the variablef is smaller than N_(grant) (step S426). When the variable f is smallerthan N_(grant) (step S426, YES), the control parameter estimation unit28 determines whether the variable a is smaller than the candidatenumber A for the number of burst frames (step S428). When the variable ais smaller than the candidate number A (step S428, YES), the controlparameter estimation unit 28 determines whether the variable f issmaller than (N_(grant)(1−(½^(n+1))) (step S430).

When the variable f is smaller than (N_(grant)(1−(½^(a+1))) (step S430,YES), the control parameter estimation unit 28 determines whether thevariable f is greater than or equal to (N_(grant)(1−(½^(a))) (stepS431). When the variable f is greater than or equal to(N_(grant)(1−(½^(a))) (step S431, YES), the control parameter estimationunit 28 adds a detection number R[i][ProbePos] to a detection numbercounter TS_(lower)[a] (step S432). When the variable f is less than(N_(grant)(1−(½^(a))) (step S431, NO), the control parameter estimationunit 28 advances the process to step S436.

In step S430, when the variable f is greater than or equal to(N_(grant)(1−(½^(a+1))) (step S430, NO), the control parameterestimation unit 28 adds the detection number R[i][ProbePos] to adetection number counter TS_(upper)[a] (step S434). The controlparameter estimation unit 28 increases the variable a by 1 (step S436)and returns the process to step S428.

In step S428, when the variable a is great than or equal to thecandidate number A (step S428, NO), the control parameter estimationunit 28 increases the variable f by 1, updates ProbePos as follows, andreturns the process to step S426.ProbePos=(ProbePos+1)mod N _(grant)

The control parameter estimation unit 28 divides each allocation cycleinto a first half allocation cycle and a second half allocation cycle byrepeatedly performing the processing from step S426 to step S436 on eachallocation cycle and repeatedly performs a process of calculating thetotal sum of detection numbers in the first half and second half cycles.

In step S426, when the variable f is greater than or equal to N_(grant)(step S426, NO), the control parameter estimation unit 28 sets thevariable a to 0 (step S440) and determines whether the variable a issmaller than the candidate number A (step S442). When the variable a issmaller than the candidate number A (step S442, YES), the controlparameter estimation unit 28 determines whether the detection numbercounter TS_(lower)[a] is greater than or equal to TS_(upper)[a] (stepS444).

When TS_(lower)[a] is greater than or equal to TS_(upper)[a] (step S444,YES), the control parameter estimation unit 28 sets TS_(diff) to adifference obtained by subtracting TS_(upper)[a] from TS_(lower)[a].Further, the control parameter estimation unit 28 sets a threshold valueThr to a value obtained by doubling TS_(upper)[a] (step S446).

When TS_(lower)[a] is smaller than TS_(upper)[a] (step S444, NO), thecontrol parameter estimation unit 28 sets TS_(diff) to a differenceobtained by subtracting TS_(lower)[a] from TS_(upper)[a]. Further, thecontrol parameter estimation unit 28 sets the threshold value Thr to avalue obtained by doubling TS_(lower)[a] (step S448).

The control parameter estimation unit 28 determines whether theTS_(diff) calculated in step S446 or step S448 is greater than thethreshold value Thr (step S450). When TS_(diff) is smaller than or equalto the threshold value Thr (step S450, NO), the control parameterestimation unit 28 advances the process to step S454. When TS_(diff) isgreater than the threshold value Thr (step S450, YES), the controlparameter estimation unit 28 increases the burst occurrence number U[a]by 1 (step S452). The control parameter estimation unit 28 increases thevariable a by 1 (step S454) and returns the process to step S442.

Upon every division, the control parameter estimation unit 28 determineswhether the total sums of detection numbers of a first half allocationcycle and a second half allocation cycle are biased by repeating theprocessing from step S442 to step S454 and stores determination resultsin the burst occurrence numbers U[0], U[1], . . . , and U[A].

The threshold value Thr may be a value obtained by multiplying a smallerone of TS_(lower)[a] and TS_(upper)[a] by n (n>1) instead of the valueobtained by doubling the smaller one of TS_(lower)[a] and TS_(upper)[a],may be a value obtained by adding a certain value to the smaller one, ormay be a predetermined value.

In step S442, when the variable a is greater than or equal to thecandidate number A (step S442, NO), the control parameter estimationunit 28 increases the variable h by 1 (step S456) and returns theprocess to step S416. The control parameter estimation unit 28 changesthe division point N_(div)[h] by updating the variable h and repeats theprocessing from step S418 to step S456.

In step S416, when the variable h is greater than or equal to 3 (stepS416, YES), the control parameter estimation unit 28 sets the variable ato 0 (step S458) and determines whether the burst occurrence number U[a]is greater than or equal to 2 (step S460). When the burst occurrencenumber U[a] is smaller than 2 (step S460, NO), the control parameterestimation unit 28 increases the variable a by 1 (step S462) and keepsincreasing the variable a by 1 until the burst occurrence number U[a]becomes greater than or equal to 2. With the processing of step S460 andstep S462, the control parameter estimation unit 28 specifies the burstoccurrence number U[a] of a case in which a bias is detected two or moretimes in a determination made at every three division points N_(div).The detection number used in the determination of step S460 isdetermined according to the number of division points N_(div).

When the burst occurrence number U[a] is greater than or equal to 2(step S460, YES), the control parameter estimation unit 28 calculatesthe number of burst frames B (=2^(a)) on the basis of the variable a(step S464) and finishes estimation of the number of burst frames B.After estimating the number of burst frames B, the control parameterestimation unit 28 calculates the processing latency T_(latency).Calculation of the processing latency T_(latency) is the same as theprocessing from step S326 to step S330 shown in FIG. 9 according to thethird embodiment. In other words, the process of estimating the numberof burst frames according to the fourth embodiment is performed betweenstep S324 and step S326 in the processing latency estimation processshown in FIG. 9.

In the flowcharts of FIG. 15, FIG. 16, and FIG. 17 showing the processof estimating the number of burst frames, a process in which threedivision points are used is shown, but the present invention is notlimited to the case. For example, when candidate numbers for the numberof burst frames are 1, 2, and C, the control parameter estimation unit28 may determine whether the number of burst frames is 1 or 2 and thenestimate that the number of burst frames is C when the number of burstframes is not any of 1 and 2.

[Operation of Transmission-Permitted Period Start Position DeterminingUnit 22]

The transmission-permitted period start position determining unit 22 inthe fourth embodiment determines a transmission-permitted period startposition for an ONU 3 according to a traffic pattern. Specifically, thetransmission-permitted period start position determining unit 22determines a transmission-permitted period start position for eachmobile data group (burst data) which arrives at the ONU. 3 in one TI.The transmission-permitted period start position determining unit 22determines a transmission-permitted period start position on the basisof a mobile data receiving time Time[i] acquired from the cooperativeprocessing unit 21 and the number of burst frames B. Atransmission-permitted period start position for an i^(th) ONU 3 isdetermined by Equation (14).[Math. 14]Time[i]+T _(latency)+(b−1)·(N _(grant) /B)·T _(period) ,b=1,2, . . .,B  (14)

For example, when the number of burst frames is 2, thetransmission-permitted period start position determining unit 22determines (Time[i]+T_(latency)) and(Time[i]+T_(latency)+(N_(grant)/2)T_(period) to be atransmission-permitted period start position.

[Operation of Transmission-Permitted Period Length Determining Unit 23]

The transmission-permitted period length determining unit 23 in thefourth embodiment determines the number of allocation cycles requiredfor transmission of respective pieces of burst data as atransmission-permitted period length for the ONU 3. Thetransmission-permitted period length determining unit 23 notifies thenumber of allocation cycles corresponding to the number of burst framesB to the allocation amount calculation unit 24. The allocation cyclenumber N_(cycle,burst)[i] is determined by Equation (15).

$\begin{matrix}\lbrack {{Math}.\mspace{14mu} 15} \rbrack & \; \\{{N_{{cycle},{burst}}\lbrack i\rbrack} = {\min( {N_{grant},\lceil \frac{{{DataSize}\lbrack i\rbrack}/B}{D_{m\; i\; n}} \rceil} )}} & (15)\end{matrix}$

Operation in which the control parameter estimation unit 28 estimatesthe number of burst frames B before estimation of the processing latencyT_(latency) has been described, but the present invention is not limitedthereto. For example, the control parameter estimation unit 28 mayestimate the number of burst frames after temporarily estimating theprocessing latency T_(latency) and estimate the processing latencyT_(latency) again on the basis of the estimated number of burst frames.In this case, the control parameter estimation unit 28 needs not to makea determination on each of a first half allocation cycle and a secondhalf allocation cycle by using a plurality of division points N_(div)and may estimate the processing latency T_(latency) by using onedivision point N_(div).

In the OLT of the fourth embodiment, the control parameter estimationunit 28 estimates the number of burst frames, and thetransmission-permitted period start position determining unit 22 and thetransmission-permitted period length determining unit 23 determine atransmission-permitted period start position and atransmission-permitted period length on the basis of the number of burstframes. Due to these operations, the OLT can accurately determine atransmission-permitted period including an entire mobile data arrivalperiod even when an ONU 3 divides mobile data into a plurality of piecesof burst data and transmits the plurality of pieces of burst data.

According to the above-described embodiments, even when there is aprocessing latency in a lower device, a gap between pieces of mobiledata, and a fluctuation of the gap, a transmission-permitted period isadjusted, and an allocation amount corresponding to the adjustedtransmission-permitted period is determined and reported, so that theentire arrival period of the corresponding mobile data may be includedin the transmission-permitted period. In this way, it is possible toreduce the amount of mobile data that cannot be transmitted from an ONUin one TTI. Also, since the allocation amount is sequentially determinedaccording to a mobile data amount of each lower device, an excessivebandwidth is not allocated to each ONU, and the delay is not increased.

According to the above-described embodiments, a communication systemincludes terminal station device and terminal device and relays upstreamdata, which is received from a communication terminal by a lower deviceconnected to the terminal device, to an upper device connected to theterminal station device. A bandwidth allocation device allocates atransmission bandwidth of the upstream data to the terminal device. Thebandwidth allocation device may be the same device as the terminalstation device. The bandwidth allocation device is, for example, theOLTs 2, 2 a, and 2 b. The bandwidth allocation device includes atransmission-permitted period start position determining unit, atransmission-permitted period length determining unit, and a bandwidthallocation unit. The transmission-permitted period start positiondetermining unit estimates a start position of an arrival period inwhich the upstream data arrives at the terminal device from the lowerdevice. The transmission-permitted period length determining unitestimates a length of the arrival period on the basis of a data amountof upstream data that can be transmitted from the lower device to theterminal device. The length of the arrival period is atransmission-permitted period length in the terminal station device. Thebandwidth allocation unit allocates a bandwidth to the terminal deviceon the basis of the estimated start position and the estimated length ofthe arrival period. The bandwidth allocation unit is, for example, theallocation amount calculation unit 24.

The bandwidth allocation device may further include a cooperativeprocessing unit which acquires radio resource information, which isinformation on radio resources allocated to the communication terminalfor wireless communication with the lower device, from the upper deviceand calculates an arrival start time where the upstream data begins toarrive at the lower device on the basis of the acquired radio resourceinformation. The transmission-permitted period start positiondetermining unit determines a time obtained by adding at least a timespent for internal processing in the lower device to the arrival starttime as an estimated time of the start position of the arrival period.

Alternatively, the bandwidth allocation device may further include atraffic monitoring unit which monitors the traffic amount of upstreamdata received from each terminal device at the terminal station device.The transmission-permitted period start position determining unitdetects a time at which the amount of upstream user data received fromthe terminal device begins to exceed a threshold value in eachautonomous interval having the same length as a transmission timeinterval of the upstream data from the lower device to the upper deviceand treats a time obtained by adding a time difference between a starttime of the autonomous interval and the detected time in the autonomousinterval at the terminal station device as an estimated time of thestart position of the arrival period.

Also, the transmission-permitted period length determining unit treats avalue obtained by multiplying a length of a predetermined period (e.g.,allocation cycles) and a value obtained by dividing the amount ofupstream data that can be transmitted from the lower device by a minimumarrival amount, which is a minimum arrivable amount of upstream datafrom the lower device in the aforementioned predetermined period, as anestimated value of the length of the arrival period. The minimum arrivalamount is a value obtained by multiplying the amount of data that can betransmitted in an arrival period of the maximum length and a valueobtained by dividing a length of a predetermined period (e.g., anallocation cycle length) by the maximum length of an arrival period.

Also, when a value obtained by multiplying the length of thepredetermined period and a value obtained by dividing the amount ofupstream data that can be transmitted from the lower device by theminimum arrival amount exceeds a length of a transmission time intervalof the upstream data from the lower device to the upper device, thetransmission-permitted period length determining unit treats the lengthof the transmission time interval as the estimated value of the arrivalperiod.

Also, the bandwidth allocation unit may equally distribute a bandwidthavailable in a period in which at least one terminal device has anarrival period to the terminal devices having the arrival period in theperiod and equally distribute an entire bandwidth available in a periodin which any terminal device does not have an arrival period to all ofthe terminal devices in the period.

Some functions of the OLTs 2, 2 a, and 2 b in the above-describedembodiments may be implemented by a computer. In this case, a programfor implementing the functions may be recorded in a computer-readablerecording medium and may be implemented by causing a computer system toread and execute the program recorded in the recording medium. The“computer system” referred to here is considered to include an operatingsystem (OS) and hardware such as peripheral devices. Also, the“computer-readable recording medium” refers to a portable medium, suchas a flexible disk, a magneto-optical disk, a read-only memory (ROM),and a compact disk read-only memory (CD-ROM), and a storage device, suchas a hard disk incorporated in a computer system. Further, the“computer-readable recording medium” may include a network, such as theInternet, a communication line, such as a telephone line, and the likewhich dynamically hold a program for a short period, and a volatilememory inside a computer system which serves as a server or a client insuch a case and holds a program for a certain period. The aforementionedprogram may be intended to implement some of the above-describedfunctions and may be able to implement the above-described functions incombination with a program which has been already recorded in a computersystem.

Although the embodiments of the present invention have been described indetail above with reference to the drawings, the present invention isnot limited to the above embodiments. Various changes understood bythose of ordinary skill in the art can be made to configurations anddetails of the present invention within the scope of the presentinvention. Also, it is possible to implement the respective embodimentsin arbitrary combination within a consistent range.

INDUSTRIAL APPLICABILITY

The present invention can be used in a system that performscommunication in a time-division duplex manner.

REFERENCE SIGNS LIST

-   -   100, 101, 102 Communication system    -   1 Upper device    -   2, 2 a, 2 b OLT    -   3 ONU    -   4 Lower device    -   21 Cooperative processing unit    -   22, 22 a Transmission-permitted period start position        determining unit    -   23 Transmission-permitted period length determining unit    -   24 Allocation amount calculation unit    -   25 Transceiver unit    -   26 Traffic monitoring unit    -   27 Statistical processing unit    -   28 Control parameter estimation unit

The invention claimed is:
 1. A bandwidth allocation device whichallocates a bandwidth to at least one terminal device in a communicationsystem including a terminal station device and the at least one terminaldevice and relaying upstream data, which is received from acommunication terminal by a lower device connected to the at least oneterminal device, to an upper device connected to the terminal stationdevice, the bandwidth allocation device comprising: at least one memoryconfigured to store instructions; and at least one processor configuredto execute the instructions to: estimate a start position of an arrivalperiod in which the upstream data arrives at the at least one terminaldevice from the lower device; estimate a length of the arrival period ona basis of an amount of upstream data to be transmitted from the lowerdevice to the at least one terminal device; and allocate a bandwidth tothe at least one terminal device on a basis of the estimated startposition and the estimated length of the arrival period, wherein the atleast one processor is further configured to execute the instructions toacquire radio resource information indicating radio resources allocatedto the communication terminal for wireless communication with the lowerdevice from the upper device and calculate an arrival start time wherethe upstream data begins to arrive at the lower device on the basis ofthe radio resource information, and wherein the at least one processoris configured to execute the instructions to treat a time obtained byadding at least a time spent for internal processing in the lower deviceto the arrival start time as an estimated time of the start position. 2.The bandwidth allocation device according to claim 1, wherein the atleast one processor is further configured to execute the instructions tomonitor a traffic amount of upstream data received from the at least oneterminal device at the terminal station device, and the at least oneprocessor is configured to execute the instructions to detect a time atwhich an amount of upstream user data received from the at leastterminal device begins to exceed a threshold value in each autonomousinterval having a same length as a transmission time interval of theupstream data from the lower device to the upper device, and treat atime obtained by adding a time difference between a start time in theautonomous interval and the detected time in the autonomous interval tothe start time in each autonomous interval at the terminal stationdevice as an estimated time of the start position.
 3. The bandwidthallocation device according to claim 1, wherein the at least oneprocessor is configured to execute the instructions to treat a valueobtained by multiplying a predetermined length of the period and a valueobtained by dividing the amount of upstream data to be transmitted fromthe lower device by a minimum arrival amount, which is a minimumarrivable amount of upstream data from the lower device in apredetermined period, as an estimated value of the length of the arrivalperiod.
 4. The bandwidth allocation device according to claim 3, whereinthe at least one processor is configured to execute the instructions totreat a value obtained by multiplying a value obtained by dividing thepredetermined length of the period by a maximum length of the arrivalperiod and an transmittable amount of upstream data in the maximumlength of the arrival period as the minimum arrival amount.
 5. Thebandwidth allocation device according to claim 3, wherein the at leastone processor is configured to execute the instructions to treat, when avalue obtained by multiplying the predetermined length of the period anda value obtained by dividing an amount of upstream data to betransmitted from the lower device by the minimum arrival amount exceedsa length of a transmission time interval of the upstream data from thelower device to the upper device, the length of the transmission timeinterval as the estimated value of the arrival period.
 6. The bandwidthallocation device according to claim 1, wherein the at least oneprocessor is configured to execute the instructions to equallydistribute a bandwidth available in a period in which the at least oneterminal device has the arrival period to the at least one terminaldevice having the arrival period in the period and equally distribute abandwidth available in a period in which any of the at least oneterminal device does not have the arrival period to all of the at leastone terminal device in the period.
 7. The bandwidth allocation deviceaccording to claim 1, wherein the at least one processor is furtherconfigured to execute the instructions to determine whether the at leastone terminal device has upstream data to be transmitted to the upperdevice at each allocation cycle obtained by dividing a transmission timeinterval of the upstream data from the lower device to the upper deviceand estimate a processing latency in the lower device on a basis of astart time of an allocation cycle in which it is determined a largestnumber of times that upstream data to be transmitted to the upper deviceis present and a time at which the lower device receives the upstreamdata from the communication terminal, and the at least one processor isconfigured to execute the instructions to calculate an estimated time ofthe start position on a basis of the estimated processing latency andthe time at which the lower device receives the upstream data from thecommunication terminal.
 8. The bandwidth allocation device according toclaim 7, wherein the at least one processor is configured to execute theinstructions to: recursively divide allocation cycles in thetransmission time interval into a first half allocation cycle and asecond half allocation cycle, estimate a number of burst frames of theupstream data on a basis of a number of times of division of thetransmission time interval performed until a certain difference or moreis detected between an amount of upstream data transmitted in the firsthalf allocation cycle and an amount of upstream data transmitted in thesecond half allocation cycle, and calculate an estimated time of thestart position on a basis of the processing latency and the estimatednumber of burst frames and the time at which the lower device receivesthe upstream data from the communication terminal.
 9. The bandwidthallocation device according to claim 1, wherein the at least oneprocessor is further configured to execute the instructions to acquirean amount of upstream data to be transmitted to the upper device fromthe at least one terminal device at each allocation cycle obtained bydividing a transmission time interval of the upstream data from thelower device to the upper device and estimate a minimum arrival amount,which is a minimum amount of upstream data to be arrived at the at leastone terminal device in an allocation cycle, on a basis of a differencein an amount of upstream data between allocation cycles, and the atleast one processor is configured to execute the instructions to treat avalue obtained by multiplying a length of an allocation cycle and avalue obtained by dividing an amount of upstream data transmitted fromthe lower device to the at least one terminal device by the minimumarrival amount as an estimated value of the length of the arrivalperiod.
 10. A bandwidth allocation method executed by a bandwidthallocation device which allocates a bandwidth to at least one terminaldevice in a communication system including a terminal station device andthe at least one terminal device and relaying upstream data, which isreceived from a communication terminal by a lower device connected tothe at least one terminal device, to an upper device connected to theterminal station device, the bandwidth allocation method comprising:estimating a start position of an arrival period in which the upstreamdata arrives at the at least one terminal device from the lower device;estimating a length of the arrival period on a basis of an amount ofupstream data to be transmitted from the lower device to the at leastone terminal device; and allocating a bandwidth to the at least oneterminal device on a basis of the estimated start position and theestimated length of the arrival period, wherein the bandwidth allocationmethod further comprises: acquiring radio resource informationindicating radio resources allocated to the communication terminal forwireless communication with the lower device from the upper device andcalculating an arrival start time where the upstream data begins toarrive at the lower device on a basis of the radio resource information,and in the estimating of the start position of the arrival period, atime obtained by adding at least a time spent for internal processing inthe lower device to the arrival start time is treated as an estimatedtime of the start position.